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122                PRACTICAL ORGANIC CHEMISTRY
PREPARATION 35
Bacemic Acid and Mesotartaric Acid.
CH(OH).COOH
I                       + H,,0
CH(OH).COOH
Pasteur, Ann. Chim. Phys., 1848, (3)24, 442 ; 1850, (3) 28,
Dessaignes, Bull Sec. Chim., 1863, 5, 35^ ; Jungfleisch,
Soc. Chim., 1872,18, 201 ; Hollemann, Rcc. trav. chim. Pays-J&ttft
1898,17,66.                     ^
100 grms. tartaric acid.
350        caustic soda (in 700 c.c. water).
Boil the tartaric acid and caustic soda solution for three hours
in a round flask (i litre), or preferably in a tin bottle furnished with
reflux condenser. The use of a tin vessel obviates certain diffi-
culties of filtration which the solution of the silica by the action
of the alkali on the glass entails. The liquid, after boiling", is
carefully neutralised with cone, hydrochloric acid (it is advis-
able to remove a little of the solution beforehand in case of
overshooting the mark) and an excess of calcium chloride solu-
tion is added to the hot liquid. The mixture is left overrun llt
and the calcium salts filtered off at the pump, washed with
water, and well pressed.
The calcium salts are well dried on the water-bath, or a frac-
tion of the whole weight of the moist salts is taken and dritnl,
and.the total dry weight estimated. The substance is then sus-
pended in boiling water and the calculated quantity of sulplivtric
acid added, after which the mixture is boiled for an hour. 1*h<;
calcium sulphate is removed by filtration, well washed with liot
water, and the precipitate pressed down. The filtrate is concron-
trated on the water-bath until crystallisation begins. Raceuxk
acid crystallises first, and after dehydrating on the water-1:>utli
melts at 505. A further quantity is obtained on evaporation.
Yield 5060 grains.
The last mother liquors contain mesotartaric acid, m. p. 1.4 $ 
144, which is much more soluble in water than raccmic a.<:Id
To obtain a pure specimen repeated crystallisation is necessary,